The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Interests in a urea-selective catalytic reduction (urea-SCR) system that can effectively reduce nitrogen oxides (NOx) generated by a diesel engine have increased.
Such an SCR system relates to a technology using reactions of nitrogen oxides (NOx) and ammonia (NH3), and if urea is injected into an exhaust pipe, urea is converted into ammonia (NH3) through hydrolysis. The converted ammonia (NH3) and nitrogen oxides (NOx) chemically react with each other on a catalyst and are converted into water and nitrogen which are not harmful to environments and humans.
Here, an injector functions to inject ammonia water into an exhaust pipe and nitrogen composites in exhaust gases are converted into nitrogen and water (H2O) on an SCR catalyst through an oxidation/reduction reaction.
Then, an amount of injected urea is determined according to how long a current is applied to the injector. The hardware injection amount reference value of the injector may be determined when the injector is developed. However, we have discovered that the injector may inject an amount of urea that is smaller or excessively larger than a urea injection amount reference value through deterioration and repeated operations thereof as the injector is used, which may dissatisfy a reference intended in an SCR catalyst chemical reaction when the injector is developed. If an amount of urea smaller than a reference value is injected, the exhaust gas rules cannot be satisfied, and when urea is excessively injected, the urea that has not chemically reacted is discharged to a rear end of a muffler so that the muffler generates ammonia smells and contaminations.